Catalysis is, essentially, speeding up a chemical reaction by adding another compound, which is not consumed in the process. Okay, so how does this work? A chemical reaction is essentially nothing else than rearranging some atoms, chopping up compounds and fusing them back together into different compounds. Molecules do not like being chopped up, and this process costs energy. As an example, consider a bucket of gasoline, with plenty of oxygen around. This gasoline would love to be nothing but carbon dioxide and water. However, under normal atmospheric conditions, the heat in the gasoline and oxygen is not enough to cut up the bonds, and nothing happens. Now, if heat, in the form of perhaps a spark, is supplied, there is enough energy to get the reaction going, and the heat generated by the reaction keeps it going.

So, heat might help in overcoming the energy barrier, needed to chop up the molecules before they can be rearranged, to start a reaction. Make stuff hot enough, and it may start to react. However, just heating up stuff has two disadvantages. Firstly, it is not selective, meaning that many reactions will go faster, not just the one you wanted to go faster. Increasing the speed of the remove-stain-from-favorite-blouse reacting can be done by heating, but this may also carbonize said blouse, which is probably not intended. Secondly, heating is expensive in terms of energy cost. So, as an alternative of using heat to overcome the energy barrier, we just lower the barrier. This is the principle behind catalysis.

A catalyst can reduce the energy barrier by forming an intermediate compound with one of the reactants. As an example, consider a catalyzed reaction from reactants A and B to product C with catalyst X:

A + X -> AX

B + AX -> ABX

ABX -> CX

CX -> C + X

Often, X is a solid, and an effective catalysis requires a large surface area. This, incidentally, is the cause of the rather impressive diet coke fountains that can be obtained by tossing a Mentos in them. Less spectacularly, have you ever noticed the bubbles in your soda always form at surfaces? Another good thing to note is that X may only be a catalyst for some reactions, but not for others. This makes it possible to selectively allow some reactions, and not allow others.

Lowering the energy may make a reaction practically possible, and it may also make it go a lot faster. The reason for this is a bit of statistical physics I won't go too deeply into. Essentially, particles with a certain temperature don't all have the same energy; rather, there is a statistical distribution, in which some particles have an energy that is below average, and some have an energy that is above average. For energies well above the average energy, the typical case, the amount of particles decreases exponentially. Hence, decreasing the energy barrier exponentially increases the reaction speed. This has something to do with the so-called Boltzmann Factor. This has many practical applications, ranging from massive industrial reactors to cleaning your house.

A case that deserves special mention are the biological catalysts known as enzymes. These often ultra-specialized catalysts make the complex reactions that drive life possible at temperatures only slightly above room temperature. Using catalysis, your body is able to burn fat and sugar at 37 degrees C rather than the few hundred degrees C it would need using fire.

In summary, the subject of catalysis is about selectively making reactions occur at lower temperatures. This is of fundamental importance for many industrial processes, and for life itself. A major part of modern chemistry and physics is about synthesizing catalysts.

A process by which reaction occurs in the presence of certain agents which were formerly believed to exert an influence by mere contact. It is now believed that such reactions are attended with the formation of an intermediate compound or compounds, so that by alternate composition and decomposition the agent is apparenty left unchanged; as, the catalysis of making ether from alcohol by means of sulphuric acid; or catalysis in the action of soluble ferments (as diastase, or ptyalin) on starch.